CYCLICITY IN THE EGRET MEMBER (KIMMERIDGIAN) OIL SOURCE-ROCK, JEANNE-DARC-BASIN, OFFSHORE EASTERN CANADA

The origin of the observed variability in lithology, total organic car bon and petrophysical properties of the Egret Member (source rock inte rval) in the Jeanne d'Arc Basin, offshore eastern Canada is examined. Detailed analyses of petrophysical logs indicate that the Egret Member is cyclic. Th ree different orders of cycles, recognizable on well lo gs, occur in the Eg ret Member. The large- and medium-scale cycles are correlatable among wells. The estimated cyclicities of the large- and medium-scale cycles fall into the Milankovitch-like cycle bands, sugg esting that the depositional cycles are the product of orbitally force d sea-level and climatic changes and implying that Egret Member deposi tion lasted at least 1.65 million years. Using chronological informati on drawn from sedimentary cycles, both spatial and vertical (temporal) variations in sedimentation rate are examined for the member. A corre lation exists between low sedimentation rates and high total organic c arbon values in this basin. It is most probable that the organic-rich layers were deposited during times of high sea-level stands and warmer periods.